Polar Vortex: Temperatures Fall Far, Fast

Meteorologists called it “weather whiplash” — a drop of roughly 50 degrees in a matter of hours that took temperatures from 55 in Central Park on Monday morning to a record low of 5 overnight and an expected high on Tuesday of only 10. The last time temperatures in New York fell that much in such a short time, Warren G. Harding was in the White House.

The reason was a mix of atmospheric ingredients that came together to give New York a precipitous, once-every-few-decades swing.

It began with the polar vortex, an elliptical-shaped pattern of frigid winds blowing west to east and centered on the North Pole.

“The vortex is normally very stable and keeps air bottled,” said James E. Overland, a scientist with the National Oceanic and Atmospheric Administration.

In the last week, though, a kink developed in the vortex’s winds, delivering arctic air to the Plains and the Midwest, forcing warmer air out of the way.

That cold air, a giant cottony blur on the weather maps, drove temperatures down to 32 degrees below zero in Fargo, N.D., on Monday, and 25 below in Comertown, Mont. Weather watchers recorded some of the coldest temperatures in years in places as far south as Nashville, where the temperature was 8 degrees at 6 p.m. and was expected to fall to 4 overnight.

In New York, Monday was a day of rapid change. Last week’s snow melted, or was chased away by early-morning rain. Thermometers that began the day in the 50s dropped through the 40s and kept sinking.

“It’s unusual, but it does happen,” said David Stark, a meteorologist with the National Weather Service at its office in Upton, N.Y., on Long Island. “The only difference in the 1920s, it went from the low 80s to the 20s.”

In March 1921, three weeks after President Harding’s inauguration in Washington, the temperature in Central Park dropped 56 degrees in 14 hours. The reading at 2 p.m. on March 28 was 82 degrees in Central Park, according to Weather Service records. Then a cold front blew in, and by midnight, the temperature had sunk to 34. It kept falling. By 6 a.m., the thermometer was at 26.

Scientists and meteorologists say one possible reason for such a sharp temperature drop was that the kink in the winds came later in the winter this year than in some previous years.

“It does so over Canada all the time,” said Thomas Herrington, a professor of ocean engineering at Stevens Institute of Technology. “To come this far south, it usually takes a push from another system, usually a warmer air system over Alaska or Greenland.”

The kink created a trough of cold, dry air in the Plains and Midwest. At the same time, outside the trough, warm moist air was brought up from the south. As the kink traveled eastward across the country, the warm air was quickly replaced by the cold, and the mercury fell, sometimes startlingly fast.

“It just so happens that the air this time has managed to grow unusually cold,” said Jeff Masters, director of meteorology with the website Weather Underground.

Weather Underground’s historian, Christopher C. Burt, said temperature drops like the one forecast for New York were not unprecedented. “You go back 100 years, and you’ll see a lot of times when this has happened,” he said.

Drops tend to be more rapid and extreme in the Midwest and Plains than on the East Coast. In the nation’s midsection, there is little to stop the onrushing Arctic air, and the Rocky Mountains tend to hem the cold air in.

This can create a “Blue Norther,” a temperature drop of dozens of degrees in a few hours. On Nov. 11, 1911, in Oklahoma City, for instance, the temperature plummeted from 83 degrees in the afternoon to 17 at midnight.

“It’s pretty rare that you’d have the equivalent of a Blue Norther over the East Coast,” Mr. Burt said.

Dr. Overland said the changes to the polar vortex had become more common in the past five years, leading to suggestions by him and others that climate change in general, and the decline in Arctic sea ice in particular, may play a role. But most researchers say there is not enough data to conclude that anything other than normal climate variability is involved.

David A. Robinson, New Jersey’s state climatologist and a professor at Rutgers, said the huge one-day temperature swing was not particularly surprising given the other weather extremes of recent weeks.

“We’ve had this amplified pattern for the past six weeks or so,” he said. “With it, we’ve had record warmth. We’ve had record cold. The fact is it’s happened, and we don’t know exactly why.”

Justin Gillis contributed reporting.

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